I pre-assembled my short block today to check everything out, 383 roller block, new Merc crank, new Scat Pro- comp rods & new Mahle pistons. The problem I encountered is the clearances are too tight. Mains average .018 and rods .020. I'm using Clevite MS-909H on the mains ad CB-663 HN on the rods.

I can't see resizing new rods and honing the block again. Could it be the coating?
I remember a thread on here but I can't find it, about using another bearing and mixing them to get clearance. I'm open to all new bearings if someone knows how to handle this.

Thanks in advance, I've always had to tighten up clearances, this too tight thing is new to me!

I believe speed pro and king bearing make an .001x bearing, thinner shell more clearance. Use 1 half to gain .0005

Why do you think that is too tight?
1999 Service numbers
Rods - .0010 -.0030"
Mains - #1- .0010 - .0020"
#2-4 - .0010-.0025"
#5 .0025-.0035" (Though most came from the factory closer to .0020")

Are you using a forged crank? If not "P" bearings are nicer to the crank. Plus you don't need radius relief with a stock crank.
Andy

is this a cast crank or steel..yes the coating adds thickness..i hat
e coated bearings..

yep,thats how ya do it.

i use the clevite h series bearings,you can run a tighter clearance with a thinner oil.my 2012 honda accord uses 0-20 oil.

Something else you can try you have a 50/50 chance is to move the bearings around > I mean change the bearing into a different rod Lets say from no. 3 to no. 5 rod . I agree with rest of the guys. Have you used a mic. on the rods to see how close they were machined? How are you checking you clearances ? We need a little more info.

Forged crank, micronite coated, I mic'd the rods and crank and plastigaged multiple times with moving the bearings around. They all stayed pretty close. I would like to see 2.5 on the rods and 3 on the mains.
If this were for a daily driver I would run it, but not comfortable in the boat. It was the "X" bearing I was looking for.
Thanks.